Gloss is an image or substrate attribute that describes how much specular reflection is observed from a surface of a substrate. Specular reflection is the mirror-like reflection of light from a surface, in which light from a single incoming direction is reflected in a single outgoing direction. Because the surface of the substrate is not always perfectly flat, the light reflected from the surface of the substrate is not similar to what would generally be reflected from a mirror. When a surface of a substrate is rough, the percentage of the light that is reflected as specular reflection is less. In general, the rougher the surface, the lesser the chance of the reflected light is going to travel in the direction of the specular reflection. By varying the roughness of the surface, different types of finishes may be achieved.
Generating a differential gloss image using a laser glossing imager to overlay a gloss image on an existing printed image is limited by print speed and image contrast. For example, a toner or ink image that absorbs laser energy from a laser glossing imager is pulse-heated to a temperature above the melting point of the toner or ink for short period of time. Typical laser imagers used for ink-based digital printing, for example, have power capabilities that are barely sufficient to produce differential gloss images at half of a speed of printing, e.g., the toner or ink image on which the gloss image is to be printed.